Process of preparing viscose solutions



Patented Nov. 24, 1925. UNITED STATES PATENT a-orrlce.

ELIE S. HUMBOLDT, OF OAKLAND, CALIFORNIA, ASSIGNOR TO THE PACIFIC LUMBER COMPANY, OF SAN'FRANCISCO, CALIFORNIA, A CORPORATION OF MAINE.

PROCESS OF PREPARING VISCOSE SOLUTIONS.

No Drawing.

To all whom. it 4mg concern:

Be it known that I, ELIE S. HUMBOLDT, a citizen of the United States, residing at Oakland, in the county of Alameda and State of California, have invented certain new and useful lmprowments in aJProcess of PreparingViscose Solutions, of which the following isa specification.

This invention relates to the proper ripening and purification of viscose solutions of fairly homogenous composition to be used in the manufacture of films, generally for any. purpose whatsoever for which a viscose solution may be used and particularly for stretch spinning of filaments through large apertures in the making of artificial or viscose silk.

In the making or spinning of such filaments it is well known that viscose, i. e, cellulosesodium-xanthate, cannot be used freshly prepared in the ordinary methods of spinning filaments in strong coagulating baths unless it has been mixed with various salts which modify its properties." When viscose is stored away and allowed to age or ripen there is a gradual degradation of the cellulose molecule and the Xanthate molecule grows heavier and more complex until 'it finally coagulates' and reverts to cellulose hydrate.

Although during the degradation process there comes a time when the viscose is easily coagulable and thus can be spun and worked into the required shapes, yet at no time does it possess a homogenous composition since the ripening process is one of gradual and continuous transformation. Moreover, the process of degradation produces a corresponding weakening of the spun filaments and it is often difficult to get rid of the impurities left in them except by a long and drastic treatment.

It is known that the ripening can be hastened by careful heating, and that the impurities contained in the raw viscose solution can be eliminated by precipitation and washing, but these processes as generally conducted are uncertain, for the reason that no attempt has been made to control or check such ripening, and my improvement consists essentially of bringing the viscous to any required degree of ripening by the application of heat andof then immediately precipitating the solut on preferably by a cold precipitating bath, and whereby the Application filed November 26, 1923. Serial No. 677,179.

ripening'of the solution is at once arrested at a known degree of its progress, and it is preferably further stabilized by immediate shredding and washing.

I have discovered that it is possible through proper application of the improvement above mentioned to modify the treatment forthe purification of raw viscose so as to produce as may be desired, either a product containing a cellulose molecule "of magnitude C to C ready for immediate spinning in a strong acid bath according to the usual practice, or a product may beproduced in which the cellulose is very little degraded, unfit to spin immediately in the ordinary way, but adapted to stretch spinning through large orifices in weak and appropriate coagulating baths. In either case the solution of cellulose is sufiiciently pure for most purposes and the final product needs but very little after treatment.

My mode of procedure is as follows Soda-cellulose made at a low temperature without excess of sodium hydroxide and well ripened to perfect mercerization is treated with carbon bisulphide until well gelatinized and then dissolved in water to form a solution containing about 10 to 12% of cellulose, at a temperature not exceeding 0 6., care being exercised that the solution or suspension is as perfect as possible.

lf ripened viscose is desired, the above raw viscose is heated by suitable means at a temperature of to C. with constant stirring until a'sample ,coagulates immediately when dropped into -a-saturated solution of sodium bicarbonate, and it is then precipitated with a cold precipitation bath. -The heating necessary will requirefrom to 1 hours, according to conditions such as ripeness of soda cellulose, the temperature during the making of the solution, etc.

if it is desired to produce a viscose in which the cellulose is but very little degraded, the rnediately without heating, while the precipitation bath is used either cold or lake warm as necessary, according to conditions;

For coagulation or recipitation, various ill) precipitation is carried on im- 1W agents may be employs such as alcohol, carlllll tions to be adjusted for best results, according to the Working conditions and the routine of manufacturing.

The best results are obtained when enough bicarbonate is used to saturate anyalkali freed-in the precipitation, and very often the addition of a small amount of sodium sulphite hardens the precipitate. For highly ripe viscose the addition of a little bisulfite of sodium towards the end of the reaction insures the production of the desired result.

About 2.5 to 3 times the amount of co agulating medium to that of the original viscose should be used, keeping the mass well stirred throughout the process to produce a fine shredding of the gelatinous mass, and subsequent easy washing of the impurities.-

When the coagulation is complete the mass is drained and washed with cold 5% sodium chloride or sodium sulfate solution until all the colored impurities are eliminated. The xanthate is then pressed strongly to a cellulose content of 10 to 14% and then dissolved in dilute sodium hydroxide to the required percentage for spinning.

I If the raw viscose has not been heated the purified viscose; would not be-satisfaetory for immediate spinning in a strong acid bath,-but willproduce very goodfilaments when stretchedfrom openings about 1 millimeter in diameter through a suitable spinning bath. On the other hand, if the raw Viscose has been heated the resulting product is ready for immediate spinning but will not keep very long at room temperature unless it contains a rather large amount of alkali.

In both cases the resulting filaments are clean and glossy and'their ultimate treatment is very sim le and easy.

Having thus escribed my invention and its application, I claim:

1. The rocess of preparing a viscose solution whic includes ripening it by the application of heat, arresting the. ripening by the application of a cold precipitatingbath followed by redissolving the precipitate.

2. The process of preparing a viscose solution which includes ripening it by the application of heat, arresting the ripening by the application of a cold precipitating bath followed by washing the precipitate and then redissolving the same.

3. In the making of viscose, the production of soda-cellulose at a low temperature,

treatment of the same with carbon bisulphide at a similar temperature, raising the temperature to force ripening of the viscose, and

of then checkin the ripening action.

4. In the making of viscose, the production of soda-cellulose at a low temperature, treatment of the same with carbon bisulphide at a similar temperature, raising the temperature to force the ripening of the viscose, and of checking the ripening action by precipitation of the xanthate, shredding,

precipitate until the impurities are removed.

reducing the water content of the washed precipitate and dissolving the same in an alkali to the required consistency.

7. The forced ripening of a solution of sodium cellulose xanthate by the, application of heat, arresting the ripening action by the application of a cold precipitating bath, shredding the precipitate, washing the same in'water to remove impurities, reducing the water content of 'th Cprecipitate and redissolving the same in so ium hydroxide to the required consistenc 8. The process of treatmg a solution of sodium cellulose xanthate which comprises preparing the same at atemperature not exceedin 20 0., ripening the same'by a raise of temperature, precipitating 'the ripened xanthate, shredding, and washing the precipitate in an aqueous salt solution, draining to a 10 to 14% Water content, and dissolving the precipitate in sodium hydroxide to the required working consistency.

ELIE s. HUMBOLDT. 

